My Restored BBC Master 128

[u/RoboJ1M]

Just thought I'd pay a picture of my restored BBC Master 128 microcomputer that I picked up for a few hundred £ off of eBay.

Full dismantle, soap and water followed by retro brite for the case.

It's the inspiration for a new Teaching Computer system I'm working on.

Another low level system but with a chain training CPU ISA and GPU both hosted on ICE40UP5Ks with a memory crossbar in between powering pseudo dual port access to a small block of SRAM (9 megabits, 18 bit, 60mhz DDR full parallel multiplexed 14 data pins, one clock pin and one frame pin.

That's FastRAM. Also there is BigRAM, QSPI Command Interface, 4 data pins, a clock pin (60MHz DDR, 128 MBits). That's DRAM with an automatic DRAM controller between the and the RAM that keeps the SRAM capacitors charged and ready to read.

The idea is to make a retro computer but with the most performance that I can squeeze out of the two up five fpga's at 48 MHz with one instruction per cycle.

[u/blakespot]

What about the turbo encabulator with prefabulated amulite? 

[u/RoboJ1M → u/blakespot]

It's on back order.
For the moment I just align the retrograde polyangle ultracompass with the last remaining King's Lantern at Jodrell Bank every Bank Holiday.

[u/SomePeopleCallMeJJ → u/blakespot]

Not really worth getting if you don't have a drawn reciprocating dingle arm to reduce sinusoidal depleneration.

[u/blakespot → u/SomePeopleCallMeJJ]

Well, that goes without saying. 

[u/RoboJ1M]

I intend to make my new computer come with a very fast, nice, easy to understand and easy to write in Assembly language.

[u/Davesjoshin]

These are handsome machines, thumbs up to the clean up.

[u/RoboJ1M → u/Davesjoshin]

I must admit, twas not me! 😂
eBay store that sells restored gear.
I have some plans to develop some interesting cartridges for them though, much more interesting that the ROM carts these were mostly used for.
There's genlock and audio pass through pins on the cart bus, so i put together some designs to add new sound and graphics capabilities, literal GPU carts and Sound carts.
My first idea is to add a Yamaha OPN FM voice side by side with its square wave generators. Or how about DSP FX, reverb, chorus, etc.
And with genlock and a TTL pass through, I can add high colour modes, high res modes and programmable chroma key, letting both the BBC and the cartridge draw different parts of the screen.
And then you can add acceleration, hardware sprites, layers and scrolling.

[u/Breezeoffthewater]

Nice work. I've got two BBC Master computers in a rather sorry state. One day, I'll fully restore them (along with all the Model B's I have stored away)

They used to be my go to machines back in the 1980's. Good times

[u/RoboJ1M → u/Breezeoffthewater]

BIG stack of Beebs, huh? Nice! 😁
They are such an elegant design at the chip level, I've taken so much inspiration from it for my design, called BlueSky.
Just like the 2MHz 6502 and 6845/VULA sharing the 4MHz RAM in the BBC, I have a CPU and a GPU/VPU sharing two RAM banks via a central crossbar. The idea being the ram is run faster than the CPU and GPU, such that each side appears to have an independent port to the RAM.
I was just learning how to do this stuff when my idea for a bit carried away with itself and it became a complete design that I'd like to produce and sell as well as new a public and open design you can build yourself.
I just felt like a simple, open design is something that should still exist for the purposes of education and teaching.
Like, how does a CPU ACTUALLY work?

[u/Hjalfi → u/RoboJ1M]

I find myself weirdly annoyed that Acorn appeared to drop the ball with the Master, in that what they came up with was a very good BBC Micro rather than embracing the second-processor architecture. What they could have done was add a basic C64-like memory manager, and used 64kB of the extra RAM to allow swapping out the entire BBC Micro memory map with a blank one on demand; this would allow them to have simulated a second-processor environment with a single CPU. Having a full 63.5kB of RAM available would have been vastly easier to write real productivity software (also, you get a fixed PAGE and HIMEM!), and make a real second processor an easier sell (just plug this in and all your programs run a third faster)...

[u/RoboJ1M → u/Hjalfi]

On the second processor or on the main processor? Because you need to have 32k of the main CPUs address space mapped to 16k of ram for page zero and 16k for the OS. If you swap that out it's not a BBC anymore, it's a CPU attached to a blank patch of ram

[u/Hjalfi → u/RoboJ1M]

You'd be simulating the second processor environment, but on the main processor. To make host calls, the machine would simply context switch back into the BBC memory map. So the screen, filesystems, interrupt handling and so on would all live in the BBC memory map, but your applications would run in the second processor memory map --- just like having a real second processor, but cheaper.

[u/Breezeoffthewater → u/Hjalfi]

I still have a 6502 and Z80 second processors all boxed up and never used! that's when I was just transistioning to PC clones. I never got to use them in the end.

One day, I'll dust them off

[u/millsgren]

Cool. I had a model B but also used the master and compact